Method for implementing wide area Centrex

ABSTRACT

The present invention discloses a method for implementing Wide Area Centrex (WAC), wherein the long number and short number corresponding relationship of the WAC users is set and saved. The method includes: routing the call initiated by a user to a soft-switch; receiving by the soft-switch the call information the calling user sends; after determining that the calling user is a WAC user based on the calling number, the soft-switch determining the route to the called user based on the call information and completing the call. The WAC, covering the Public Switched Telephone Network (PSTN)/Public Land Mobile Network (PLMN) user and the Next Generation Network (NGN) user of different physical networks, can be implemented by using the method of the present invention without any software or hardware change to the switches in the existing network.

FIELD OF THE INVENTION

The present invention relates to the technique of the switch incommunication system, and particularly, to a method for implementingWide Area Centrex.

BACKGROUND OF THE INVENTION

It is common knowledge that 80% of the income of telecommunication comesfrom 20% of the clients, namely the big clients. Now, the importance ofthe big clients to the operators is self-evident in the increasingtelecommunication competition. The enterprises and big clients requirehigh-standard quality of telecommunication services due to their specialservice needs, and the focus of competition among operators forattracting the big clients is to provide value-added services capable ofbringing significant benefits to the big clients while satisfying thebasic requirement of voice service and data service, and the CentralExchange (Centrex) service is one of the popular value-added services.

The so called Centrex service regards some aggregative users as a usergroup and provides the group with various service functions, such ascalling each other in the group with short numbers. Herein, the shortnumber is the number valid only in the group and usually has fewerdigits. At present, however, the Centrex service provided by astored-program control switch is only allowed to be used within theexchange. That is to say, extensions can call each other with shortnumbers only when they are in the same user group of one exchange. Usersbelonging to one aggregative client but covered by Centrex of differentexchanges have to call each other with the uniform numbers in the PublicSwitched Telephone Network (PSTN), which is a long number.

However, users belonging to one aggregative client but covered bydifferent exchanges may desire to call each other with short numbers aswell. Then Wide Area Centrex (WAC) needs to be provided for theaggregative client. WAC is to combine the Centrex of different switchnodes into a virtual cross-region private network through physical andsignaling connection. Though such a private network is dispersed inregions, it is similar to a single Centrex in performance and use. Thatis to say, WAC users also have two numbers: a long number and a shortnumber. Besides the basic calling and complementary services of thePSTN, the users in the group can enjoy many special complementaryservices similar to those provided by a Private Automatic BranchExchange (PABX), such as calling each other via short numbers within thegroup. Further, a telephonist can be configured in each group to assistout-group, into-group and in-group calling. A call center can also beestablished to assist the calling of many Centrex groups simultaneously.

WAC service can be implemented through the Intelligent Network(IN) inthe prior art, namely the so called 600 service, in which multiplecities are covered by the intelligent network such that users could calleach other with short numbers. Such a service is in fact a result ofcombining WAC and the Virtual Private Networking (VPN) of the INservice.

The structure of a WAC system implemented through the IN is illustratedin FIG. 1, including users 10, 11 and 12, Local Switch (LS) 22, ServiceSwitch Point (SSP) 30, and Service Control Point (SCP) 40, wherein LScan be classified into two types, one is LS21 which supports attributejudgement and number transformation for WAC users, and the other is LS22which does not support attribute judgement and number transformation forWAC users. In addition, SCP 40 includes the long number and short numbercorresponding table, which is used for saving the correspondingrelationship between the long numbers and the short numbers of the WACusers.

The process of using LS21 which supports attribute judgment and numbertransformation for WAC users in the prior art is hereinafter describedin detail: Provided that user 10, who has the short number 5001 and longnumber 5550888, wants to call a cross-region user 12 who has the shortnumber 7001 and long number 7770888 in the same group. At this time,user 10 may dial the short number 7001 to LS21 directly. After LS21finds that the short number is not a short number of its own exchange,it adds 600N1N2 before the short number automatically, which changes theshort number into 600N1N2+7001, then directs and connects the 600 routeto SSP 30. After detecting the intelligent call, SSP 30 reports theintelligent call to SCP 40. SCP 40 finds the long number being called is7770888 based on the long number 5550888 of the calling and the shortnumber 7001 of the called. Then, SCP 40 instructs SSP 30 to connect tothe long number being called 7770888. Thereafter, the connecting processbetween SSP30 and the called is the same as an ordinary call.

The process of using LS 22 which does not support attribute judgment andnumber transformation for WAC users in the prior art is as follows:Provided that user 11, who has the short number 6001 and long number6660888, wants to call a cross-region user 12 who has the short number7001 and long number 7770888 in the same group. At this time, user 11needs to dial 600N1N2+7001 to LS 22, then LS 22 directs and connects the600 route to SSP 30. Thereafter, the process is the same as above.

Besides being implemented by using the IN, WAC can be implemented by themethod of distributed number memorization and transformation. In such acase, the inter-exchange relay signaling of the LS is the IntegratedServices Digital Network (ISDN) User Part (ISUP) while theinter-exchange support for the extended Signaling Connection ControlPart (SCCP) is required. As shown in FIG. 2, suppose that WAC isconfigured for two LS, every LS uses the switch of Internet ServiceProvider (ISP) board, and all the long number and short numbercorresponding tables of the WAC users in the group are saved in theswitches used. The switches set up the communication path of SCCP viathe PSTN. When an in-group call is made, the number of the group and theshort number are sent to the ISP to inquire about the corresponding longnumber. The inquired long number may be the number of the same exchangeor that of another exchange, and an in-exchange call or a cross-exchangecall is implemented after an analysis of the long number. Herein, routedata of the Message Transfer Part (MTP) ,which enable the telephonestation to conduct cross-switch management of the data of the WAC usersin the group and obtain phone bills across exchange by means of SCCPsignaling ,are configured between the LS,.

In such a manner of implementation, the user data of each LS in the WACneed to be maintained and synchronized. The specific process of the datamaintenance is as follows: When the user data in the WAC group arerevised by a Background Administration Module (BAM) of a switch of an LSexchange and the WAC telephone station, the long number and short numbercorresponding table of the WAC group on the ISP board of the LS isrevised. Meanwhile, the long number and short number correspondingtables relating to the WAC group on the ISP boards of other exchange arealso revised through SCCP signaling so as to implement automaticcross-exchange user data maintenance. The specific process of the datasynchronization is as follows: The long number and short numbercorresponding table of the WAC group on the ISP board will trigger thefunction of synchronized checking manually or periodically, whichcompares the long number and short number corresponding table with thosesaved in other exchanges within the WAC group to determine whether thetables are the same. If the tables are not the same, synchronizedrevision is performed, respectively, according to the data of theexchange to which the user belongs.

At present, WAC service can already be provided for users of PSTN,Public Lands Mobile Network (PLMN), and Next Generation Network (NGN)simultaneously.

SUMMARY OF THE INVENTION

In practical use the first method, in which the long number and shortnumber transformation is implemented through the IN, needs to save dataand consume a great deal of resources in the intelligent SCP, resultingin heavy workload and high cost. The second method requires the existingswitches to extend the ISUP interfaces, and corresponding data must beconfigured in all the switches, which involves changes to the switchesof different manufacturers and different versions in the network, makingquick implementation and wide application thereof difficult.

The reason for this situation is mainly that both methods require a lotof changes to the existing network without making full use of thetechniques and facilities of the existing network.

In view of the above, this invention provides a method for implementingWide Area Centrex (WAC), in which the WAC covering the PSTN/PLMN usersand the NGN users of different physical networks, is implemented withoutthe need for any software or hardware changes to the switches in theexisting network, wherein the corresponding relationship between longnumbers and short numbers of WAC users is set and saved, and the methodincludes:

routing a call initiated by a calling user to a soft-switch, receivingby the soft-switch the call information initiated by the calling user,determining, based on the calling number, that the calling user is a WACuser before deciding the route to the called user based on the callinformation and completing the call.

When the calling WAC user is a NGN user and the called WAC user is aPSTN/PLMN user; the step of routing the call initiated by a user to thesoft-switch is that the NGN user dials the short number of the calleduser, and initiates the call to the soft-switch; the step of receivingby the soft-switch the call information the calling user initiates isthat the soft-switch directly receives the short number of the calleduser which the NGN user dials; and the step of determining the route tothe called user and completing the call is that the soft-switch startsits own analysis of Centrex numbers, obtains the long number of thecalled user according to the saved corresponding relationship betweenlong numbers and short numbers, routes the call to the LS to which thecalled user belongs according to the obtained long number and completesthe call.

When the calling WAC user is a PSTN/PLMN user; the step of routing thecall initiated by a user to the soft-switch is that the PSTN/PLMN userdials the out-group prefix of the WAC, and the call is routed to thesoft-switch after the LS to which the PSTN/PLMN user belongs checks anddetermines that the out-group prefix is the out-group prefix of the WAC;the step of receiving by the soft-switch the call information thecalling user initiates is that the soft-switch receives the out-groupprefix the LS sends; the step of determining the route to the calleduser and completing the call is that the soft-switch obtains the data ofthe Centrex according to the calling number, starts its own analysis ofCentrex numbers to determine that the call is an out-group call, deletesthe out-group prefix and starts the process of handling an out-groupcall of the IP Centrex service.

When the calling WAC user is a PSTN/PLMN user; the step of routing thecall initiated by a user to the soft-switch is that the PSTN/PLMN userdials the long number of the called user, and the call is routed to thesoft-switch by the LS to which the PSTN/PLMN user belongs according tothe pre-planned routing data; the step of receiving by the soft-switchthe call information the calling user sends is that the soft-switchreceives the long number of the called which the LS sends; the step ofdetermining the route to the called user and completing the call is thatthe soft-switch gets the data of the Centrex according to the callingnumber, starts its own analysis of Centrex numbers to determine that thecall is an out-group call, and then starts the process of handling anout-group call of the IP Centrex service.

When the corresponding relationship of long number and short number ofthe WAC users is saved in the long number and short number correspondingtable, wherein the long number and short number corresponding table issaved in the soft-switch, or saved in the peripherals of thesoft-switch. Alternatively, the corresponding table is saved in a remotedatabase, and then the method further includes: the soft-switchaccessing the remote database directly or via proxy. Herein, the proxyis the local database.

The method further includes that the switches belonging to the same WACservice group determine the short number prefix and the out-group prefixof the WAC group through negotiation.

The main difference between the methods of the present invention and theprior art can be found by comparison: the WAC is implemented based onthe soft-switch in the present invention, wherein the long number andshort number corresponding table of the WAC is saved in the soft-switchor an external database it can access. Both the call of a PSTN/PLMN userand that of a NGN user in the group are routed to the soft-switch. Thelong number and short number transformation is performed according tothe long number and short number corresponding table after an analysisof the calling number, and the call is routed to the called useraccording to the result of the transformation.

Such a difference between the methods brings apparent benefits, namelythe soft-switch can be connected to the switches in the existing networkby using the standard ISUP/Telephone User Part (TUP) protocol becausethe long number and short number transformation is performed in thesoft-switch. So no development and upgrading of the existing switchesare needed for implementing the WAC service. Furthermore, the method ofthis invention based on soft-switch makes a full use of the process forhandling a call of the IP Centrex, having less impact on the existingnetwork while achieving high efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure for implementing WAC through the IN of theprior art;

FIG. 2 shows the structure for implementing WAC through distributednumber memorization and transformation in the prior art;

FIG. 3 is a schematic showing the structure for implementing WACcovering PSTN/PLMN users and NGN users in accordance with an embodimentof the present invention;

FIG. 4 is a flow chart of a NGN user in the WAC group dialing shortnumber to call a PSTN/PLMN user in the group in accordance with anembodiment of the present invention;

FIG. 5 is a flow chart of a PSTN/PLMN user in the WAC group dialing anout-group prefix to call a PSTN/PLMN user or a NGN user in accordancewith an embodiment of the present invention;

FIG. 6 is a flow chart of a PSTN/PLMN user in the WAC group calling aPSTN/PLMN user or a NGN user directly in accordance with an embodimentof the present invention;

FIG. 7 is a schematic of adopting an external additional informationdatabase in an embodiment of the present invention;

FIG. 8 is a schematic of adopting a narrowband switch instead of thesoft-switch in an embodiment of the present invention;

FIG. 9 is a schematic of using a local database and a remote database inan embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

To make the method and advantages of the present invention moreapparent, the present invention will hereinafter be described in detailaccording to the accompanying drawings.

First, the NGN IP Centrex service will be described. The NGN IP Centrexservice is a Centrex service built on a soft-switch system. Soft-switchis the core equipment used for dealing with call signaling, performingcall control and implementing service in the NGN. Compared with theCentrex service provided by the traditional PSTN switch, new propertiesare added to the Centrex service provided by the system of soft-switchbecause the bearer of the system of soft-switch is a wideband IP datanetwork. The user in a NGN IP Centrex group can be all kinds of users,such as ordinary users of voice service, multimedia users and etc.within the soft-switch domain, or PSTN/PLMN users connected with thesoft-switch domain.

The basic principle of the present invention is: the WAC long number andshort number corresponding table is saved in a place where thesoft-switch can access; calls of the WAC users from PSTN/PLMN and NGNare all routed to the soft-switch, and whether the procedure forhandling a WAC call is started or not is determined by recognizing thenumber of the calling; if it is determined to start the procedure, thefunction of long number and short number transformation, the function ofnumber analysis and the function of call routing are performed. The WAClong number and short number corresponding table can be put in thesoft-switch directly, or in the peripherals of the soft-switch, or in aremote database which the soft-switch can access via proxy.

Hereinafter, the implementation of the WAC service covering PSTN/PLMNusers and NGN users will be described with reference to FIG. 3.

As shown in FIG. 3, the long number and short number corresponding table60 covering PSTN/PLMN users and NGN users is embedded in soft-switch 50in the NGN; LS23 of the PSTN domain and LS24 of the PLMN domain areconnected to soft-switch 50 by means of trunk equipment, respectively;besides, WAC telephone station 70 used for uniformly maintaining thedata of the group is also connected to soft-switch 50; user 13 is a WACuser of the NGN domain, user 14 is a WAC user of the PSTN domain, anduser 15 is a WAC user of the PLMN domain.

When implementing WAC based on soft-switch 50, the calls of NGN users inthe same WAC group are handled as ordinary IP Centrex call withoutmodification, because the call control and service implementation ofcalls from NGN users are originally performed by soft-switch 50. As faras PSTN/PLMN users in the WAC group are concerned, no hardware orsoftware change to the relevant LS is needed while it is only needed toroute the calls of WAC users to soft-switch 50 by means of dataconfiguration. Calls from PSTN/PLMN users within a WAC group are mainlydivided into 3 types: the short number Centrex call in the group, theCentrex call with out-group prefix, and the ordinary call. Aftersoft-switch 50 determines that the call is a call from a PSTN/PLMN userin the WAC group through the process of recognizing the group of thecalling, the call will be handled according to the uniform procedure ofhandling an ordinary IP Centrex call, thus making a full use of theexisting IP Centrex procedure.

Procedures of various services are described in detail hereinafter.

The procedure of a NGN user in the WAC group calling a NGN user in thesame WAC group: use the existing procedure for handling a call in IPCentrex service.

The procedure of a NGN user in the WAC group calling a NGN user who isnot in the same WAC group: use the existing procedure for handling acall in IP Centrex service.

The procedure of a NGN user in the WAC group dialing an out-group prefixto call a PSTN/PLMN user: use the existing procedure for handling anout-group call in IP Centrex service.

The procedure of a NGN user in the WAC group dialing a short number tocall a PSTN/PLMN user in the same WAC group includes the following stepsas shown in FIG. 4:

Step 401: The NGN user in the WAC group takes up the telephone and dialsthe short number of a PSTN or PLPM user within the group, sending a callto the soft-switch. Herein, the NGN user is the calling user and thePSTN or PLMN user is the called user.

Step 402: Soft-switch 50 finds the call is an in-group call sent from aWAC user by the process of analyzing and recognizing the calling numberin itself after receiving the short number the NGN user has dialed.

Step 403: Soft-switch 50 starts its own Centrex number analysis,searching the long number and short number corresponding table 60 savedin itself to get the long number of the called PSTN or PLMN user.

Step 404: After the long number is obtained, soft-switch 50 routes thecall to the LS to which the called PSTN/PLMN user belongs according tothe obtained long number to complete the call.

The procedure of a PSTN/PLMN user in the WAC group dialing the out-groupprefix to call a PSTN/PLMN user or a NGN user includes the followingsteps as shown in FIG. 5:

Step 501: The PSTN/PLMN user in the WAC group takes up the telephone anddials the out-group prefix of the WAC.

Step 502: The LS to which the PSTN/PLMN user in the WAC group belongsdetects that the called prefix is an out-group prefix of a call in theWAC, and routes the call to soft-switch 50.

Step 503: Soft-switch 50 determines that the call is a call sent from aPSTN/PLMN user of the WAC by the process of analyzing and recognizingthe calling number, and gets the relevant data of the Centrex user.

Step 504: Soft-switch 50 starts its own procedure of Centrex numberanalysis according to the called prefix received, and finds that this isan out-group call with the out-group prefix, then deletes the out-groupprefix.

Step 505: Soft-switch 50 starts the process for handling an out-groupcall in IP Centrex service.

It should be noted here that the switches in the same WAC group need todetermine the short-number prefix and the out-group prefix of the WACgroup through negotiation. Herein, the short-number prefix of the groupmeans the prefix of the short number of the WAC users, and generallyspeaking, it is used in number analysis when the user calls or the useris called.

The procedure of a PSTN/PLMN user in the WAC group calling a PSTN/PLMNuser or a NGN user directly is shown in FIG. 6:

Step 601: The PSTN/PLMN user in the WAC group takes up the telephone anddials the long number of the PSTN/PLMN user or the NGN user.

Step 602: The LS to which the PSTN/PLMN user in the WAC group belongsroutes the call to soft-switch 50 according to the pre-configuredrouting data.

Step 603: Soft-switch 50 determines that the call is a call sent from aPSTN/PLMN user of the WAC by the analyzing process to recognize thecalling number, and gets the relevant data of the Centrex user.

Step 604: Soft-switch 50 starts its own Centrex number analyzingprocedure according to the called prefix received, and finds that thisis an out-group call with out-group prefix. This step is different fromStep 504 in that the out-group prefix need not be deleted.

Step 605: Soft-switch 50 starts the procedure for handling an out-groupcall in IP Centrex service.

In addition, there can be the following substitutions of theabove-mentioned modes of implementation.

One substitution is: the long number and short number correspondingtable is not saved in the soft-switch but in the peripherals of thesoft-switch. As shown in FIG. 7, the long number and short numbercorresponding table is saved in the additional information database in apreferred embodiment of the present invention. The additionalinformation database is connected with the junction tandem exchangethrough Interface 1 and the additional information database in thepresent embodiment is a local database. The soft-switch is used as atransit exchange in the embodiment as shown in FIG. 7.

Another substitution is: the narrowband switch in the existing networkis used instead of the soft-switch to realize WAC. In a preferredembodiment of the present invention as shown in FIG. 8, a network nodecomposed of the narrowband switch in the existing network instead of thesoft-switch is connected with the LS, and the narrowband switch is alsoconnected with an additional information database. The long number andshort number corresponding table is saved in the additional informationdatabase and the additional information database in the presentembodiment is a local database.

Yet another substitute method as shown in FIG. 9 is: when the longnumber and short number corresponding table is not found in the localdatabase, the soft-switch can access a remote database directly throughInterface 3, or access the cross-region database via the local databasethrough Interface 4. When Interface 4 is adopted, the local databaseacts as a proxy to search and obtain the additional information of thecalling from the remote database, then passes the search result to theswitch. Herein, both the local database and the remote database are theadditional information database in which the long number and shortnumber corresponding table is saved.

In the above three substitutions, Interface 1, Interface 3 and Interface4 use standard interface in general. Obviously, the interface standardagreed by both sides through negotiation can also be used as long asinformation interaction can be implemented between the two sides.

Although the present invention has been illustrated and describedaccording to preferred embodiments, it is apparent to those skilled inthe art that there can be various changes in form and details, withoutdeparting from the scope and spirit of the invention as defined in theappended claims.

1. A method for implementing Wide Area Centrex (WAC), wherein acorresponding relationship between long number and short number of theWAC users is set and saved, the method comprising: routing a call acalling user initiates to a soft-switch; receiving by the soft-switchcall information the calling user initiates and determining that thecalling user is a WAC user by analyzing and recognizing a callingnumber; determining a route by the soft-switch to a called WAC userbased on the call information and completing the call; wherein the WACis implemented by trunk equipment, when said calling user is a PublicSwitched Telephone Network (PSTN) or Public Land Mobile Network (PLMN)user; and the step of routing the call the calling user initiates to thesoft-switch comprises: the PSTN or PLMN user dialing an out-group prefixof the WAC or a long number of the called user, and a Local Switch (LS)to which the PSTN or PLMN user belongs routing the call to thesoft-switch; the step of the soft-switch receiving the call informationthe calling user sends comprises: the soft-switch receiving theout-group prefix or the called long number that the LS sends; the stepof determining the route by the soft-switch to the called user andcompleting the call comprises: the soft-switch obtaining the data of theCentrex according to the calling number, starting its own analysis ofCentex numbers to determine that the call is an out-group call, andstarting the procedure for handling an out-group call in IP Centrexservice; wherein the WAC implemented by means of trunk equipment refersto routing the call the calling user initiates by the LS to which thePSTN or PLMN user belongs to the soft-switch by means of the trunkequipment.
 2. The method according to claim 1, wherein when said callingWAC user is a Next Generation Network (NGN) user and said called WACuser is a PSTN or PLMN user; the step of routing the call the callinguser initiates to the soft-switch comprises: the NGN user dialing ashort number of the called user, and initiating the call to thesoft-switch; the step of receiving by the soft-switch the callinformation the calling user initiates comprises: the soft-switchreceiving the short number of the called user that the NGN user dials;the step of determining the route by the soft-switch to the called userand completing the call comprises: the soft-switch starting its ownanalysis of Central Exchange (Centrex) numbers, obtaining the longnumber of the called user according to the saved long number and shortnumber corresponding relationship, and routing the call to a LS to whichthe called user belongs according to the obtained long number andcompleting the call; wherein the WAC is implemented by means of trunkequipment refers to routing the call by the soft-switch to the LS towhich the called user belongs by means of the trunk equipment.
 3. Themethod according to claim 2, wherein the long number and short numbercorresponding relationship of the WAC users is saved in a long numberand short number corresponding table.
 4. The method according to claim2, further comprising: the switches belonging to the same WAC servicegroup determining the short number prefix and the out-group prefix ofthe WAC group through negotiation.
 5. The method according to claim 1,wherein the long number and short number corresponding relationship ofthe WAC users is saved in a long number and short number correspondingtable.
 6. The method according to claim 5, wherein the long number andshort number corresponding table is saved in the soft-switch.
 7. Themethod according to claim 1, further comprising: the switches belongingto the same WAC service group determining the short number prefix andthe out-group prefix of the WAC group through negotiation.
 8. The methodaccording to claim 1, wherein the long number and short numbercorresponding relationship of the WAC users is saved in a long numberand short number corresponding table.
 9. The method according to claim 1wherein the long number and short number corresponding relationship ofthe WAC users is saved in a long number and short number correspondingtable.
 10. The method according to claim 1, wherein when the PSTN orPLMN user dialing the out-group prefix of the WAC, the step of routingthe call the calling user initiates to the soft-switch furthercomprises: the LS to which the PSTN or PLMN user belongs routing thecall to the soft-switch after the LS determining through detection thatthe out-group prefix is the out-group call prefix of the WAC; and beforestarting the procedure for handling the out-group call in IP Centrexservice, the method further comprises: deleting the out-group prefix.11. The method according to claim 10, wherein the long number and shortnumber corresponding relationship of the WAC users is saved in a longnumber and short number corresponding table.
 12. The method according toclaim 10, further comprising: the switches belonging to the same WACservice group determining the short number prefix and the out-groupprefix of the WAC group through negotiation.
 13. The method according toclaim 1, wherein when the PSTN or PLMN user dialing the long number ofthe called user, the step of routing the call the calling user initiatesto the soft-switch further comprises: the LS to which the PSTN or PLMNuser belongs routing the call to the soft-switch according to apre-configured forting data.
 14. The method according to claim 13,wherein the long number and short number corresponding relationship ofthe WAC users is saved in a long number and short number correspondingtable.
 15. The method according to claim 14, wherein the proxy is alocal database.
 16. The method according to claim 13, furthercomprising: the switches belonging to the same WAC service groupdetermining the short number prefix and the out-group prefix of the WACgroup through negotiation.
 17. A soft-switch, configured to implement amethod comprising: receiving call information a calling user initiatesand determining that the calling user is a Wide Area Centrex (WAC) userby analyzing and recognizing a calling number; determining a route to acalled WAC user based on the call information and completing the call;wherein a corresponding relationship between long number and shortnumber of the WAC users is set and saved, when said calling user is aPublic Switched Telephone Network (PSTN) or Public Land Mobile Network(PLMN) user, the soft-switch is further configured to implement themethod comprising: receiving an out-group prefix or a called long numberthat a Local Switch (LS) to which the PSTN or PLMN user belongs sends;obtaining the data of the Centrex according to the calling number,starting the soft-switch's own analysis of Centex numbers to determinethat the call is an out-group call, and starting the procedure forhandling an out-group call in IP Centrex service.
 18. The soft-switchaccording to claim 17, wherein when the soft-switch receives theout-group prefix that the LS to which the PSTN or PLMN user belongssends, the soft-switch is further configured to implement the methodcomprising: deleting the out-group prefix before starting the procedurefor handling the out-group call in IP Centrex service.